Pressure control for variable pressure monotube boiler

ABSTRACT

An apparatus for regulating the pressure in a monotube boiler in accordance with the changes in the pressure drop across the associated throttling valve. A reversible motor which drives a rotary air-and-fuel control member is reversibly energized in response to movement of a piston in a cylinder connected across the throttling valve. The piston actuates a lever extending between a pair of respective motorenergizing microswitches carried on a swinging bracket which is coupled to the air-andfuel control member. The cylinder has a fixed second piston, relative to which the cylinder is movable in response to excessive boiler tube pressure, this cylinder movement acting to energize the motor in a direction to reduce the supply of fuel and air and thereby bring down the boiler tube pressure.

United States Patent Carter et al.

1 51 Sept. 30, 1975 Primary E.\'aminer-Robert G. Nilson ABSTRACT Anapparatus for regulating the pressure in a monotube boiler in accordancewith the changes in the pressure drop across the associated throttlingvalve. A reversible motor which drives a rotary air-and-fuel controlmember is reversibly energized in response to movement of a piston in acylinder connected across the throttling valve. The piston actuates alever ex tending between a pair of respective motorenergizingmicroswitches carried on a swinging bracket which is coupled to theair-and-fuel control member. The cylinder has a fixed second piston,relative to which the cylinder is movable in response to excessiveboiler tube pressure, this cylinder movement acting to energize themotor in a direction to reduce the supply of fuel and air and therebybring down the boiler tube 12 Claims, -6 Drawing Figures [5 PRESSURECONTROL FOR VARIABLE PRESSURE MONOTUBE BOILER [76] Inventors: J. WarneCarter, 2206 Weeks Pk. Ln., Wichita Falls, Tex. 76308; J. Warne Carter,Jr., Neville Apt. No. [571 8, Burkburnett, Tex. 76354 [22] Filed: Feb.22, 1974 [2]] Appl. N0.: 444,918

[52] US. Cl 137/94; 60/664; 122/448 R [51] Int. Cl. ..F01D 17/08 [58]Field of Search 122/448 R, 448 S; 126/351; 137/94; 236/25 A; 60/664 [56]References Cited UNITED STATES PATENTS 2,079,165 5/1937 Gorrie 122/44812' x 2,081,948 6/1937 Michel et al 1 1 122/448 S 2,143,820 l/l939 Payn1 1 137/94 X 2,777,513 1/1957 Cooper 137/94 X pressure.

FOREIGN PATENTS OR APPLICATIONS 686,483 l/l940 Germany 137/94 724077-25Muygf 68 ExPn/vae'e U.S. Patent Sept. 30,1975 Sheet 2 of2 3,908,686

PRESSURE CONTROL FOR VARIABLE PRESSURE MONOTUBE BOILER This inventionrelates to control apparatus for steam power systems, and moreparticularly to apparatus for regulating the pressure in a water tubesteam boiler of the variable pressure type.

A main object of the invention is to provide a novel and improvedcontrol system for regulating the pressure in a monotube boiler of thevariable pressure type, the system involving relatively simplecomponents, being reliable in operation, and providing a high degree ofoverall thermal efficiency by reducing throttling of the steam acrossthe main throttle valve of the system.

A further object of the invention is to provide an improved fuel-and-aircontrol apparatus for a monotube boiler of the variable pressure type,the apparatus operating to provide a relatively narrowly controlleddefinite pressure drop across the throttle valve associated with theboiler by utilizing the pressure drop across the throttle valve tocontrol the fuel firing rate of the boiler, the apparatus involvingrelatively inexpensive components, being easy to install, being operableover relatively long periods of time with a minimum amount of humansupervision, and providing a substantial improvement in overall thermalefficiency of the system by minimizing the amount of throttling of thesteam across the throttle valve.

A still further object of the invention is to provide an improvedpressure control system for a monotube boiler of the variable pressuretype, the apparatus acting to reduce the stress on the parts of thesystem such as the boiler tube, water pump and packing, and the like, bypreventing the boiler from operating continuously at maximum pressure,the apparatus being highly sensitive to changes in pressure across thethrottle valve of the system, and operating rapidly to control thepressure in response to such changes, whereby to maintain the pressuredrop across the throttle valve within specified limits over a wide rangeof load conditions, and the system being arranged to shut off the fuelflow automatically when the boiler pressure becomes excessive.

A still further object of the invention is to provide an improvedcontrol device for use with a variable pressure monotube boiler of atype intended for use as the power plant of a vehicle, the controlapparatus being relatively compact in size, having relatively fewparts,and acting to automatically allow changes of pressure differentialacross the throttle valve of the system at different power settings,thereby providing good throttle response for low pressure settings, forexample, in urban driving, and also providing good efficiency for cruisepower settings.

Further objects and advantages of the invention will become apparentfrom the following description and claims, and from the accompanyingdrawings, wherein:

FIG. 1 is an end elevational view, partly in cross section, of afuel-and-air regulating apparatus for a monotube boiler constructed inaccordance with the present invention, said view being takensubstantially on the line 1-1 of FIG. 2.

FIG. 2 is a front elevational view, partly in vertical cross-section, ofthe apparatus of FIG. 1, said view being taken substantially on the line22 of FIG. 1.

FIG. 3 is an enlarged longitudinal cross-sectional view taken throughthe pressure-responsive cylinder assembly employed with the apparatus ofFIGS. 1 and 2, said view being taken substantially on the line 3-3 ofFIG. 2.

FIG. 4 is an enlarged fragmentary front elevational view of an endportion of the pressure-responsive cylinder assembly showing thesecurement through the main supporting bracket of one of the piston rodsemployed in the pressure-responsive view assembly, said view being takensubstantially on the line 4-4 of FIG. 1.

FIG. 5 is a schematic diagram, diagrammatically illustrating thelocations of the conduit connections associated with the controlapparatus with respect to the main throttle valve of the system withwhich the apparatus of FIGS. 1 to 4 is employed.

FIG. 6 is a schematic diagram showing the electrical connections in atypical installation involving the apparatus of FIGS. 1 to 4.

A steam power system employing a variable pressure boiler, for example,a boiler of the monotube type, has several important advantages over aconstant pressure boiler, but also has problems which must be overcomeif it is to be successfully used for an application requiring theability to quickly and effectively respond to a wide range of changes inloading, for example, when the system is employed as the power plant foran automobile. The major advantage of a variable pressure boiler are thefollowing:

1. There is an increase in overall thermal efficiency.

In a constant pressure boiler it is necessary to operate continuously atthe maximum pressure that would be ever required by the steam expander,and therefore when the expander is operating at a low power output, themain control valve must throttle a relatively large pressure drop, or acontrol means must be provided to vary the engine cut-off, neither ofwhich is very efficient.

2. There is less stress on the boiler tube, the water pump and theassociated packing, because the boiler is not operated continuously atthe maximum pressure.

The main disadvantage heretofore encountered with the use of a variablepressure boiler is the delay in throttle response. There is a delaybetween the time the throttle or fuel firing rate is increased and thetime that the boiler pressure will start to increase. Incomparison, in aconstant pressure boiler the pressure isalready present, and therefore acertain amount of stored energy is available in the boiler, although nota very great amount since only a relatively small amount of water ispresent in the entire boiler, for example, of the order of one quart ina typical installation of the scale contemplated by the presentinvention.

The primary concept of the present invention is to narrowly control thepressure drop across the throttle valve in a manner such thatsubstantially instantaneous throttle response is provided, this pressuredrop being employed to control the fuel firing rate.

To increase the pressure, the fuel flow rate may be increased, and atthe same time, the waterflow rate may be increased. For example, in atypical embodiment of the present invention illustrated diagrammaticallyin FIG. 5, there may be a pressure drop of the order of 250 pounds as?square inch across the throttle valve 11 when the fab] flow is low,namely, when the expander; showri ill l2, is in an idling condition.This pressure al b proximately llBBllhds per square inch when the'fuelflow is at a ill'tlillllilllh: In the apparatus, presently to betll'ibfe ases substantially linearly to apdescribed, as the throttlevalve 11 is opened. the pressure across this valve decreases and thisdecrease in pressure is employed to operate a spring-loaded piston,which in turn is suitably linked to increase the fuel firing rate. Theapparatus includes a feed back" mechanism which senses and controls therate at which the fuel firing rate is increased or decreased. A smalldecrease in pressure differential across the throttle valve 11 resultsin a small increase in the fuel firing rate, whereas a large decrease insaid pressure differential will result in a large increase in the fuelfiring rate. The reverse action occurs for increase in said differentialpressure.

The apparatus presently to be described also incorporates a novelfail-safe device, being a second spring'loaded piston which starts tomove when the boiler pressure becomes excessive, for example, atapproximately 1,900 pounds per square inch in the typical embodimentconsidered herein, and which acts to shut off the fuel flow. By the timethe boiler pressure has reached an upper safe limit, (for example, 2,100pounds per square inch in the typical embodiment herein illustrated anddescribed,) the fuel flow is reduced to its minimum amount and is thenshut off. This fail-safe (or auxiliary pressure response device) isarranged and interlinked with the main piston device in a unique mannersuch that it allows a predetermined, measurable linear movement (stroke)of the main piston while allowing identical linear travel for theauxiliary pressure response device independently one with respect to theother, but not allowing simultaneous movement of both.

As will be presently seen, with the control system of the presentinvention a variable pressure boiler system of inherent reliability canbe successfully employed, the system including the required pressuredifferential across the throttle valve necessary for instant throttleresponse. Furthermore, as will be presently explained, the apparatus maybe adjusted to provide a larger pressure differential across thethrottle valve for urban and stop-and-go driving, and a lower pressuredifferential across the throttle valve for highway cruise conditions.

Referring to the drawings, 13 generally designates a boiler suitablymounted on a vehicle, said boiler including a boiler tube 14. Secured toone end of the boiler 13 is a supporting plate 15 on which is mounted arotary air damper member 16 for controlling the supply of combustion airto the boiler. For example, the member 16 may comprise a drum formedwith an aperture in its periphery, shown at 17, which cooperates with aconcentrically arranged inner fixed drum member 18 having an aperture 19arranged so that it can register with the aperture 17 and also arrangedso that its degree of registering may be varied as member 16 rotates.Thus, with the configuration illustrated in FIGS. 1 and 2, the supply ofcombustion air to the boiler decreases when the member 16 rotates in aclockwise direction, as viewed in FIG. 2, whereas the air supplyincreases when the member 16 rotates in a counterclockwise direction.

Mounted on the peripheral portion of the member 16 is a fuel control cam20 having a suitably contoured edge 21, which is engaged by a roller 22journaled on the end of a follower arm 23 which is rotatably mounted ona shaft 24 and which is provided with a cable guide pulley 25 aroundwhich extends a fuel con-- to the arm 23 and the other end beingconnected to a movable fuel control valve element contained in theboiler fuel valve assembly, shown at 28. The fuel supply rate controlmechanism thus described is arranged to increase the fuel ratesimultaneously with an increase of boiler combustion air, namely, withcounterclockwise rotation of the member 16, and conversely to decreasethe fuel supply rate simultaneously with clockwise rotation of airdamper member 16. The damper member for purposes herein is described asbeing operated electrically. However, any equivalent operating means maybe employed for this purpose, such as an electro-mechanical means, ahydraulic means, a pneumatic means or a direct mechanical means, withinthe contemplation of the present invention.

In the typical example disclosed herein the damper member 16 is operatedby a reversible electric motor 29, whose shaft is drivingly connected toa pulley element 30 around which is engaged an endless belt 31 which isdrivingly engaged in a peripheral groove 32 provided on air dampermember 16, as shown in FIG. 1. Motor 29 may be energized from a suitablesource of current, such as a battery 33, respective directional windingsof the motor being connected to-said battery through opposite forwardand reverse microswitches 34 and 35, which are operated in a mannerpresently to be described.

Generally designated at 36 is a pressure-responsive valve assemblycomprising a cylindrical main body 37 which is slidably engaged with aconformably shaped guide member 38 secured on the plate member 15. Theleft end portion of the cylindrical body 37, as viewed in FIG. 2, isprovided with a cup-shaped end plug element 39 which is threadablysecured in the left-end portion of the cylinder body 37 and which isformed with a central aperture 40 through which slidably extends apiston rod 41 whose outer end portion is adjustably secured to anupstanding lug 42 formed integrally with the plate member 15 andextending perpendicularly thereto, as is clearly shown in FIG. 4. Therod 41 extends through an aperture in the lug 42 and is adjustablysecured to the lug by opposite clamping nuts 43, 43 threadably engagedon the end portion of rod 41 on opposite sides of lug 42.

The right-end portion of the cylinder assembly 36, as viewed in FIG. 2,comprises a cylindrical segment 44 having a reduced left-end portion 45,as viewed in FIG. 2, which is threadably secured in the right-endportion of the main cylinder body 37. The segment 44 is generallycup-shaped and has a relatively thick left-end wall portion 46 and isprovided with a cover plug 47 threadably engaged in its right-endportion, as viewed in FIG. 2. The left-end portion of the segment 44 hasa main axial bore 48 in which is sealingly and slidably disposed themain piston element 49.

Piston element 49 is formed with the axial hollow boss to which isrigidly connected an axially extending rod 50 which extends sealinglyand slidably -through the central portion of end plug 47. The boss 100is received in a flanged bearing cup 101. Plug 47 is formed with anannular seat 102. A relatively heavy coiled spring 61 is interposedbetween end plug 47 and cup 101, bearing at its right end on the seat102 and at its left end on the flange of cup 101, as viewed in FIG. 2,biasing the piston element 49 leftwardly.

Rigidly secured on rod 41 is a relatively small piston 53 which extendsslidably and sealingly through a central bore 52 in wall portion 46 andwhich is loosely received in the axial bore of piston element 49. Wallportion 46 is formed with an integral collar element 103 defining anannular seat 104 therearound. A flanged annular bearing cup member 105is provided on the rod 41, the flange portion: thereof being received inthe seat 104. A spherical bearing washer 106 is provided between the cupmember 105 and the left end of piston element 53, as viewed in FIG. 2.

A coiled spring 57 surrounds rod 41 and bears between end plug 39 andthe flange of cup member 105, exerting leftward biasing force oncylinder body 37 relative to the fixed rod 41.

Piston element 49 is formed with an annular collar element 107 in whichis diametrically secured a transverse pin 108 which extends through alongitudinal slot 109 formed in piston 53, as shown in FIG. 3, thuslimiting the axial movement of piston 49 relative to piston 53.

The spaces on the opposite sides of the main piston element 49 areconnected across the throttle valve 11. Thus, a conduit 65 connects theoutlet end of the boiler tube 14 to the space at the left-side of pistonelement 49, as viewed in FIG. 2, and another conduit 67 connects theconduit 68 leading from the throttle valve 11 to the expander 12 to thespace at the right side of the piston element 49, namely, to theinterior of the hollow segment 44. Thus, the pressure differentialacross the conduits 65 and 67 acts on the piston element 49 in a mannertending to move it rightwardly in the bore 48 against the opposing forceexerted by coil spring 61. Likewise. the boiler pressure acting throughthe conduit 65 is exerted between the main piston 49 and the smallerpiston element 53 and acts to move the entire cylinder assemblyrightwardly relative to the fixed rod member 41 against the biasingforce of the coil spring 57.

Rigidly secured to the main supporting plate upwardly and rightwardlyadjacent the cylinder segment 44 and extending transverse thereto is apost member 70. Thus, as shown in FIG. 1, the post member 70 may beprovided with a reduced end stud 71 which extends through an aperture inplate 15 and is clamped thereto by a clamping nut 72. Rotatably andsupportingly mounted on post member 70 is a sleeve member 73 to which isrigidly secured a generally triangular bracket member 74 to the oppositelower corner portion of which are secured the opposing microswitches 34and 35. Rotatably mounted on the sleeve member 73 is .another sleevemember 75 to which is rigidly secured a depending spring arm 76 whichextends between the inwardly facing operating plunger elements of themicroswitches 34 and 35 and which depends sufficiently downwardly so asto be engaged by the outer end portion of the rod element 50, as shownin FIG. 2, the arm 76 being biased against the outer end portion of therod 50 by a coil spring 77. One end of spring 77 is anchored to plate 15and the other end of said spring comprises an arm 78 which bears againstarm 76 and biases arm 76 in a clockwise direction, as viewed in FIG. 2.

Axially secured to the left-end portion of post member 70 is a pivotbolt 79 on which is rotatably engaged a collar element 80 which isreceived in the left-end portion of sleeve member 73. A cup-shapedmember 81 receives the left-end portion of sleeve member 73 and collarelement 80 and is rigidly secured thereto by a fastening screw 82.Rigidly secured to the cupshaped member 81 is an arm 83. Arm 83 is thusrigidly connected to sleeve member 73 and is rotatable relative to thefixed post member 70.

A follower extension arm element 84 is adjustably secured to the arm 83by the provision of a longitudinal slot 85 in arm 83 and a pair ofclamping screws 86, 86 engaged through slot 85 and threadably engagedwith arm 84, whereby arm 84 may be adjustably secured longitudinallyrelative to arm 83. The upper end of arm element 84 is provided with apin 88 slidably and rotatably engaging in a radial slot 89 provided inthe circular face of member 16.

It will thus be seen that rotation of the member 16 will generate acamming action between slot 89 and pin 88 transmitted by the connectedarm segments 84 and 83 to the sleeve member 73, which will in turn swingthe bracket member 74 around the pivot post in the same direction as thearm segments 83 and 84. This changes the position of the opposingmicroswitches 34 and 35, but the swinging movement of the depending arm76 extending therebetween is produced only by the action of the pistonrod element 50, which is in turn produced by the pressure differentialchanges across the throttle valve 11 acting on piston element 49 againstthe biasing force of the spring 61.

In operation, when the pressure differential across the throttle valve11, namely, the differential across the conduits 65 and 67 becomes greatenough to overcome the'force exerted by the coil spring 61, the piston49 will move rightwardly, as viewed in FIG. 2, and compress spring 61further until the force exerted by the spring and the force on thepiston are equal. This piston movement causes rod 50 to move arm 76rightwardly,

as viewed in FIG. 2, and thereby close microswitch 35. This energizesmotor 29 in a direction to rotate member 16 clockwise, as viewed in FIG.1, namely, in a direction to reduce the area of the air damper aperturedefined by the overlapping openings 17 and 19 and which also reduces thefuel input rate to the boiler. This clockwise rotation of member 16 actsto rotate the arm 84-83 in a counterclockwise direction, as viewed inFIG. 2, and thus moves the bracket element 74 in a direction away fromarm 76 until microswitch 35 is allowed to open and thereby deenergizemotor 29. A reverse action occurs when the pressure differentialdecreases, allowing spring 61 to push piston 49 leftwardly, the arm 76following the leftward movement of the rod 50 by the action of thespring 77, whereby switch 34 closes and energizes motor 29 in adirection to rotate member 16 counterclockwise, as viewed in FIG. 2, tothereby increase the air damper aperture and the fuel input rate. Theapparatus will, therefore, act to stabilize the pressure differentialacross the throttle valve 11 under various loading conditions and over apredetermined pressure differential range.

It will be noted that a small movement of piston 49 produces arelatively small change in the damper opening, whereas a large movementof said piston produces a large change in the damper opening. The changein the damper opening is thus proportioned in accordance with the amountof movement of the piston element 49.

It will be noted that the feed-back ratio, namely, the magnitude ofresponse to changes in pressure differential across throttle valve 11,can be regulated by adjusting the position of the extension element 84with respect to the arm 83, namely, by adjusting the effective length ofthe composite arm 84-83.

The apparatus also operates to prevent an excessive pressure build-up inthe boiler tube 14. Thus, when the steam pressure in the conduit 65,connected to the outlet end of boiler tube 14, becomes high enough (forexample, about 1,900 pounds per square inch in a typical embodiment) toovercome the force of the coil spring 57, the cylinder body 37 movesrightwardly, as viewed in FIG. 2, relative to the piston 53, andcompresses spring 57 further until the force exerted by the spring andthe force on the piston 53 are equal. This movement of the cylinder 36causes rod 50 to swing arm 76 counterclockwise, as viewed in FIG. 2, toclose microswitch 35 and to produce the action described above, namely,movement of member 16 in a direction to close the air damper apertureand reduce the fuel input rate. The apparatus responds rapidly enough sothat by the time the boiler pressure reaches its upper safe limitingvalue of pressure, for example, 2,100 pounds per square inch in thetypical embodiment above mentioned, the air damper aperture becomescompletely closed and the fuel input rate is reduced sufficiently toallow the boiler pressure to decrease to a safe value. When the boilerpressure has returned substantially to its normal operating pressurevalue, the apparatus will stabilize at a normal operating pressure.

From the above description, it will therefore be seen that the automaticcontrol apparatus above described acts to substantially maintain aspecified pressure differential across the throttle valve 11 over a widerange of operating conditions and also acts to prevent an excessivebuild-up of boiler pressure. At different power settings, the pressuredifferential allowed across the throttle valve is automatically changedso that the apparatus provides good throttle response for low pres suresettings (for example, in urban driving) and good efficiency for cruisepower settings.

While a specific embodiment of an improved system for regulating thepressure in a water tube steam boiler has been disclosed in theforegoing description, it will be understood that various modificationswithin the spirit of the invention may occur to those skilled in theart. Therefore, it is intended that no limitations be placed on theinvention except as defined by the scope of the appended claims.

What is claimed is:

1. In combination, a variable pressure steam boiler, combustion fuelcontrol valve means connected to the boiler to supply a controlled rateof combustible fuel thereto, variable control throttle valve meanshaving different power settings connected to the output of the boiler tocontrol the pressure on a utilizing device supplied by the boiler,pressure differential-sensing means connected across said throttle valvemeans, and means operatively coupling said pressure differential-sensingmeans to said fuel control valve means.

2. The structural combination of claim 1, and an adjustable air dampermember, and means simultaneously operating said fuel control valve meansand said air damper member.

3. The structural combination of claim 1, and wherein said fuel controlvalve means is provided with a rotary control member and the meansoperatively coupling said pressure differential-sensing means to saidfuel control valve means comprises interengaging cam means driven bysaid sensing means and acting on said valve means.

4. The structural combination of claim 1, and wherein said pressuredifferential-sensing means comprises a cylinder having a movable piston,biasing means acting on said piston, and conduit means connecting thespaces on opposite sides of the piston across said throttle valve means.

5. The structural combination of claim 1, and wherein said fuel controlvalve means includes an adjustable air damper member.

6. The structural combination of claim 1, and wherein the meansoperatively coupling said pressure differential-sensing means to saidfuel control valve means comprises reversible electric motor meansdrivingly coupled to said fuel control valve means, and meanstoreversibly energize said electric motor means in accordance withchanges in the pressure differential across the throttle valve meanssensed by said sensing means.

7. The structural combination of claim 1, and auxil iarypressure-responsive means connected to the boiler, and means operativelycoupling said auxiliary pressure-responsive means to said fuel controlvalve means to proportionally reduce the fuel flow as the boilerpressure approaches a predetermined safe value.

8. In combination, a steam boiler, combustion fuel control valve meansconnected to the boiler to supply a controlled rate of combustible fuelthereto, throttle valve means connected to the output of the boiler,pressure differential-sensing means connected across said throttle valvemeans, and means operatively coupling said pressure differential-sensingmeans to said fuel control valve means, wherein said pressuredifferential-sensing means comprises a cylinder having a movable piston,biasing means acting on said piston, and conduit means connecting thespaces on opposite sides of the piston across said throttle valve means,means movably axially supporting said cylinder, and means moving saidcylinder in a direction to reduce fuel flow when the boiler pressurerises above a predetermined safe value.

9. The structural combination of claim 8, and wherein the means axiallysupporting said cylinder includes a fixed piston rod having a smallpiston axially aligned with and loosely received in an axial bore insaid first-named piston, the space on one side of the first-named pistonincluding the space between said small piston and said axial bore.

10. The structural combination of claim 9, and wherein said first-namedpiston has an annular collar surrounding said small piston which isprovided with a transverse pin, said small piston having a longitudinalslot receiving said transverse pin, whereby to limit axial movement ofsaid first-named piston relative to said small piston.

11. In combination, a steam boiler, combustion fuel control valve meansconnected to the boiler to supply a controlled rate of combustible fuelthereto, throttle valve means connected to the output of the boiler,pressure differential-sensing means connected across said throttle valvemeans, and means operatively coupling said pressure differential-sensingmeans to said fuel control valve means, wherein said pressuredifferential-sensing means comprises a cylinder having a movable piston,biasing means acting on said piston, and conduit means connecting thespaces on opposite sides of the piston across said throttle valve means,and means supporting said cylinder for axial movement,

said throttle valve means, and means operatively coupling said pressuredifferential-sensing means to said fuel control valve means, and whereinsaid fuel control valve means comprises a rotatably mounted adjustableair damper member provided with a fuel control cam and a stationary fuelvalve having a rotary control arm engaging said control cam.

l= i =l

1. In combination, a variable pressure steam boiler, combustion fuelcontrol valve means connected to the boiler to supply a controlled rateof combustible fuel thereto, variable control throttle valve meanshaving different power settings connected to the output of the boiler tocontrol the pressure on a utilizing device supplied by the boiler,pressure differential-sensing means connected across said throttle valvemeans, and means operatively coupling said pressure differential-sensingmeans to said fuel control valve means.
 2. The structural combination ofclaim 1, and an adjustable air damper member, and means simultaneouslyoperating said fuel control valve means and said air damper member. 3.The structural combination of claim 1, and wherein said fuel controlvalve means is provided with a rotary control member and the meansoperatively coupling said pressure differential-sensing means to saidfuel control valve means comprises interengaging cam means driven bysaid sensing means and acting on said valve means.
 4. The structuralcombination of claim 1, and wherein said pressure differential-sensingmeans comprises a cylinder having a movable piston, biasing means actingon said piston, and conduit means connecting the spaces on oppositesides of the piston across said throttle valve means.
 5. The structuralcombination of claim 1, and wherein said fuel control valve meansincludes an adjustable air damper member.
 6. The structural combinationof claim 1, and wherein the means operatively coupling said pressuredifferential-sensing means to said fuel control valve means comprisesreversible electric motor means drivingly coupled to said fuel controlvalve means, and means to reversibly energize said electric motor meansin accordance with changes in the pressure differential across thethrottle valve means sensed by said sensing means.
 7. The structuralcombination of claim 1, and auxiliary pressure-responsive meansconnected to the boiler, and means operatively coupling said auxiliarypressure-responsive means to said fuel control valve means toproportionally reduce the fuel flow as the boiler pressure approaches apredetermined safe value.
 8. In combination, a steam boiler, combustionfuel control valve means connected to the boiler to supply a controlledrate of combustible fuel thereto, throttle valve means connected to theoutput of the boiler, pressure differential-sensing means connectedacross said throttle valve means, and means operatively coupling saidpressure differential-sensing means to said fuel control valve means,wherein said pressure differential-sensing means comprises a cylinderhaving a movable piston, biasing means acting on said piston, andconduit means connecting the spaces on opposite sides of the pistonacross said throttle valve means, means movably axially supporting saidcylinder, and means moving said cylinder in a direction to reduce fuelflow when the boiler pressure rises above a predetermined safe value. 9.The structural combination of claim 8, and wherein the means axiallysupporting said cylinder includes a fixed piston rod having a smallpiston axially aligned with and loosely received in an axial bore insaid first-named piston, the space on one side of the first-named pistonincluding the space between said small piston and said axial bore. 10.The structural combination of claim 9, and wherein said first-namedpiston has an annulAr collar surrounding said small piston which isprovided with a transverse pin, said small piston having a longitudinalslot receiving said transverse pin, whereby to limit axial movement ofsaid first-named piston relative to said small piston.
 11. Incombination, a steam boiler, combustion fuel control valve meansconnected to the boiler to supply a controlled rate of combustible fuelthereto, throttle valve means connected to the output of the boiler,pressure differential-sensing means connected across said throttle valvemeans, and means operatively coupling said pressure differential-sensingmeans to said fuel control valve means, wherein said pressuredifferential-sensing means comprises a cylinder having a movable piston,biasing means acting on said piston, and conduit means connecting thespaces on opposite sides of the piston across said throttle valve means,and means supporting said cylinder for axial movement, means drivinglycoupling said piston to said fuel control valve means, and means movingsaid cylinder in a direction to reduce fuel flow when the boilerpressure rises above a predetermined safe value.
 12. In combination, asteam boiler, combustion fuel control valve means connected to theboiler to supply a controlled rate of combustible fuel thereto, throttlevalve means connected to the output of the boiler, pressuredifferential-sensing means connected across said throttle valve means,and means operatively coupling said pressure differential-sensing meansto said fuel control valve means, and wherein said fuel control valvemeans comprises a rotatably mounted adjustable air damper memberprovided with a fuel control cam and a stationary fuel valve having arotary control arm engaging said control cam.